Electronic display with semitransparent back layer

ABSTRACT

An electronic display includes electrically conductive layers. An active layer is disposed between adjacent electrically conductive layers. The active layer includes cholesteric liquid crystal material. At least one transparent front substrate is disposed adjacent one of the electrically conductive layers near a front of the display. A semitransparent back layer absorbs light that passes through the active layer, reflects grey light or light of a color and is light transmitting. Electronic circuitry applies a voltage to the conductive layers that enables at least one of erasing or writing of the active layer.

BACKGROUND OF THE INVENTION

This disclosure relates generally to an electronic display, for example,a writing/drawing tablet utilizing a pressure sensitive display. Ingeneral, Bistable Liquid Crystal Displays (BLCDs), and in particular,Cholesteric Liquid Crystal Displays (ChLCDs), have proven to have greatpotential to create low cost pressure sensitive displays that areefficient power consumers and that can be utilized in a number of uniquedevices.

Recently, the Boogie Board® pressure sensitive cholesteric liquidcrystal writing tablet, of Improv® Electronics has appeared on themarket in which a pointed stylus or the finger can be used to write ortrace an image on the surface of the tablet as described in U.S. Pat.No. 6,104,448. This tablet offers a considerable improvement overprevious tablet technologies in that the image can be simply andinstantly erased with the push of a button that applies a voltage pulseto electrodes in the tablet. In a cholesteric liquid crystal writingtablet, the liquid crystal is sandwiched between two substrates that arespaced to a particular gap. The upper substrate is flexible and thebottom substrate is painted with a fixed opaque light absorbing darkbackground. Within the gap is a bistable cholesteric liquid crystalwhich can exhibit two textures, an essentially transparent (focal conic)texture and a color reflective (planar) texture. The spacing of the cellgap is usually set by plastic or glass spacers that are eithercylindrical or spherical in shape. The tablet is initialized by applyingvoltage pulses to the electrodes to electrically drive the cholestericmaterial to the focal conic state. When one presses on the top substratewith a point stylus or finger, the liquid crystal is locally displaced.Flow induced in the liquid crystal changes its optical texture fromessentially transparent to a brilliant reflective color at the locationof the stylus. The reflective color contrasts well with the darkbackground of the lower substrate. An image traced by the stylus orfinger will remain on the tablet indefinitely without application of avoltage until erased. Erasure is accomplished by applying a voltagepulse to transparent conducting electrodes on the inner surface of thesubstrates that drive the cholesteric liquid crystal from its colorreflective state back to its essentially transparent state.

The above described principle is disclosed in more detail in U.S. Pat.No. 6,104,448. Polymer dispersions can be used to control the pressuresensitivity and resolution of the image as described in U.S. PatentApplication Publication No. 2009/0033811, which is incorporated hereinby reference. Other modes of operation and a tablet for multiple colorimages are described in this patent application publication and a meansfor select erase is disclosed in U.S. Patent Application Publication No.2009/0096942, which is incorporated herein by reference and isapplicable to the displays of the present disclosure. One mode ofoperation different from that described above is one in which the tabletis initialized by electrically driving the tablet display to the colorreflective texture with a voltage pulse or pulses. Then with acontinuous voltage applied to the electrodes of an appropriate value,one can write images by driving the cholesteric material to thesubstantially transparent texture with the pressure of a pointed stylus.This mode of operation with a color reflective background is termed ModeA whereas the other mode with an essentially transparent background istermed Mode B.

The commercial Boogie Board® writing table, operated in Mode B, has thecolor black for the fixed opaque light absorbing background. The darkblack background offers high contrast for the color reflective imagewritten on the tablet. As disclosed in U.S. Pat. No. 5,493,430, otheropaque colors may also be used for the fixed background of a cholestericliquid crystal display. The color of the background additively mixeswith the reflective color to present a different color than that of thecholesteric liquid crystal. There may be multiple colors on thebackground and those colors may be patterned. As an example, the patterncould be lines offering a lined tablet for convenience in writing textsimilar to a ruled paper tablet.

A problem with the prior art is that the background color and anybackground pattern on the tablet are fixed. One cannot change thebackground pattern; that is in the example of patterned lines, onecannot remove the lines for cases where text is not to be written. Wedisclose a different electronic display and tablet design whereby thebackground image can be changed.

BRIEF DESCRIPTION

One embodiment of this invention makes use of semitransparent inks orcolor filters for the background of the tablet. For the purposes of thispatent, the term semitransparent means: transparent to selectedwavelengths of visible light with remaining wavelengths fully orpartially absorbed. In this case, the semitransparent ink or colorfilter is used as a semitransparent light absorbing layer. The smallabsorption enhances the contrast of the cholesteric reflection when theimage is written. Also, choosing certain color combinations ofsemitransparent ink and the peak of the cholesteric reflection can yielda new color not only for the written image, but also the background. Thesemitransparency of the display enables the use of templates or patternsto be placed behind the display for tracing or coloring in on the liquidcrystal of the display. That is, coloring on the liquid crystal displayover the pattern will appear as if one colored in the pattern using acolored marker in contact with the pattern. Except that the colorreflected by the liquid crystal, the colors reflected, absorbed andtransmitted through the semitransparent back layer and the color of thepattern, will influence the colors seen by the viewer of the display.The ink coating or filter can also be used to reduce unwantedreflections between the back substrates and template. Colored templatescan be used to change the background pattern, the color of the displayand the color of the written image. In another embodiment the backgroundof the tablet is replaced by an electronic skin, waveguide, or otherdevice capable of exposing or hiding a pattern.

A first aspect of this disclosure features an electronic displayincluding electrically conductive layers. An active layer is disposedbetween adjacent conductive layers, the active layer includingcholesteric liquid crystal material. At least one transparent frontsubstrate is disposed adjacent one of the electrically conductive layersnear a front of the display. A semitransparent back layer absorbs lightthat passes through the active layer, reflects grey light or light of acolor and is light transmitting. Electronic circuitry applies a voltageto the conductive layers that enables at least one of erasing or writingof the active layer. For example, the electronic circuitry can apply thevoltage to the conductive electrodes so that the active layer is placedin a bright state, a dark state, a grey scale state or a state achievedwhen applying a write voltage Vw as described below.

Referring to specific features of the first aspect, any of the featuresof the Detailed Description may apply to the first aspect in anycombination. Further, the voltage can be applied as a voltage pulse or acontinuous voltage. A transparent back substrate can be disposedadjacent the semitransparent back layer. A portion of or an entire areaof the electrically conductive layers can be patterned into a passivematrix. The passive matrix can comprise one of the conductive layersforming rows of substantially parallel electrode lines on one side ofthe active layer and another of the conductive layers forming columns ofsubstantially parallel electrode lines on the other side of the activelayer, wherein the columns are substantially orthogonal to the rows.

Moreover, the electronic display can be in a form of a decorativeelectronic skin. Also featured is an article comprising the electronicskin selected from the group consisting of cell phone, laptop, computer,computer monitor, computer mouse, computer keyboard, television, I-pod,MP3 player, PDA, video game controller, stereo, radio, CD player,appliance, toy, headphones, clock, handheld electronic devices, key ringaccessory, shoe, purse, backpack, briefcase, computer case, computercovering, jewelry, watch, bottle, bottle lid, clothing, clothingembellishment, furniture, furniture embellishment, mobile entertainmentcase and combinations thereof.

Still further, a back pattern can be disposed behind the semitransparentback layer, wherein the back pattern is visible through thesemitransparent back layer. The back pattern can be removable andselected from the group consisting of a template of a sports field,court or arena, a pattern for a children's game, an image for childrento color, notepad lines, graph paper lines, or a menu of items that onecan choose from. The back pattern can comprise a waveguide includinglight sources disposed at an edge thereof, and light emitting portionson a surface of the waveguide enable light to leave the waveguide in apattern. The back pattern can comprises an emissive, backlit orreflective display device for displaying images.

A second aspect of this disclosure features a writing tablet includingelectrically conductive layers. At least one active layer is disposed ina gap between adjacent conductive layers. The active layer includescholesteric liquid crystal material. An outer layer of flexibletransparent material forms a writing surface. A semitransparent backlayer absorbs light that passes through the active layer, reflects greylight or light of a color and is light transmitting. The active layer isadapted to enable writing pressure applied to the writing surface toreduce thickness of the gap to form a reduced gap region in which theliquid crystal is light reflecting so as to reflect light of a color oris essentially transparent. A texture of the liquid crystal is unchangedin a non-reduced gap region. Electronic circuitry applies an erasingvoltage to the conductive layers for the active layer. The erasingvoltage enables the liquid crystal of the active layer to be placed in alight reflecting texture so as to reflect light of a color or enablesthe liquid crystal of the active layer to be placed in an essentiallytransparent focal conic texture.

Referring to more specific features of the second aspect, any of thefeatures of the first aspect, as well as any features of the DetailedDescription, may apply in any combination. Further the electroniccircuitry can apply a writing voltage to the electrically conductivelayers. The writing pressure is applied while applying the writingvoltage effective to place the reduced gap region of the active layer inthe essentially transparent focal conic texture while not changing thetexture of an unreduced gap region of the active layer.

Referring to a third aspect of this disclosure, a multicolor writingtablet includes electrically conductive layers. At least two or threeactive layers are stacked over each other each disposed in a gap betweenadjacent conductive layers. The active layers include cholesteric liquidcrystal material. An outer layer of flexible transparent material formsa writing surface. A semitransparent back layer absorbs light thatpasses through the active layer, reflects grey light or light of a colorand is light transmitting. The active layers are adapted to enablewriting pressure applied to the writing surface to reduce thickness ofthe gaps to form reduced gap regions. Electronic circuitry applieserasing and writing voltages to the conductive layers for each of theactive layers. The erasing voltage enables the liquid crystal of theactive layer to be placed in a light reflecting texture so as to reflectlight of a color or enables the liquid crystal of the active layer to beplaced in an essentially transparent focal conic texture. The writingvoltage enables writing in a color that is selected from any of theactive layers by applying the writing voltage to the conductive layersfor a non-selected active layer while applying the writing pressure tothe writing surface, enabling the reduced gap region of the non-selectedactive layer to be in the essentially transparent focal conic texture.By not applying the writing voltage to the conductive layers for theselected active layer while applying the writing pressure to the writingsurface, the reduced gap region of the selected active layer can reflectthe color of the selected active layer.

Many additional features, advantages and a fuller understanding of theinvention will be had from the accompanying drawings and the DetailedDescription that follows. It should be understood that the above BriefDescription describes the invention in broad terms while the followingDetailed Description describes the invention more narrowly and presentsspecific embodiments that should not be construed as necessarylimitations of the broad invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Illustration showing the components of a commercially availableBoogie Board® flexible cholesteric liquid crystal writing tablet of theprior art.

FIG. 2a-d : Illustrations showing a flexible display with asemitransparent medium forming a writing tablet for templates.

FIG. 3: Illustration of a writing tablet having a semitransparent backlayer with a digital display.

FIG. 4: Illustration of a writing tablet having a semitransparent backlayer with an image forming waveguide.

FIG. 5A: Photograph of a blue display having a semitransparent backlayer.

FIG. 5B: Illustration of the electronic display of FIG. 5A including thesemitransparent back layer which forms a bottom surface of the display,or a semitransparent or clear layer below the semitransparent back layerforms a bottom surface of the display; the writing tablet is shownplaced over a hand.

FIG. 6: Illustration of a writing tablet cell with a semitransparentback layer;

FIG. 7: Illustration of the voltage response curves used in describingthe invention (with voltage increasing toward the right of the figureand reflectance increasing toward the top of the figure);

FIG. 8: Schematic illustration of a double stack multicolor writingtablet with a semitransparent back layer;

FIG. 9: Reflection spectra of a writing tablet having a bluesemitransparent back layer on a yellow template.

FIG. 10: Reflection spectra of a writing tablet having a bluesemitransparent back layer on a white template.

FIG. 11 shows an article including an electronic display of thisdisclosure.

FIGS. 12a and 12b show an electronic display of this disclosureincluding a semitransparent back layer showing any removable backpattern behind it, such as one including notepad lines, for example,graph paper.

FIG. 13 shows an electronic display of this disclosure including threestacked liquid crystal layers.

DETAILED DESCRIPTION

In a cholesteric display of the prior art such as the Boogie Board®writing tablet a fixed black opaque light absorbing medium is used toenhance the contrast of the display. Referred to as the displaybackground, it is typically made by painting the backside of the lowersubstrate black. Referring to FIG. 1, this opaque coating 1 is placed onthe bottom transparent plastic substrate 2 that is coated on its othersurface with a transparent electrically conductive layer 3. Theremainder of the display includes a layer 4 of a cured dispersion ofliquid crystal, polymer and spacers, and another transparent topsubstrate 6 coated with a transparent electrical conductor 5. The bottomand top substrates are extended to create the bottom ledge 7 and topledge 8. The transparent conductive layers 3 and 5 are exposed on theledges 7 and 8, respectively, for connecting to drive electronics sothat a voltage or voltage pulses may be applied across electricallyconductive layers 3 and 5 as is necessary to initialize or erase animage or operate the display in Mode A, Mode B or select erase asdescribed in U.S. Patent Application Publication Nos. 2009/0033811 and2009/0096942, which are incorporated herein by reference in theirentireties. A drawback of prior art cholesteric writing tablets has beenthe inability to change the background of the writing or drawingsurface. For example, it is often desired to have a lined tablet as anaid for handwriting. As another example, in children's education it isoften desired to have a figure for a child to trace or to play games.

Disclosed is an electronic display (e.g., a writing tablet) thatprovides a means for changing background images with surprisingly littleloss in display contrast or brightness. A writing tablet utilizes asemitransparent back layer (e.g., a color filter) as the displaybackground. The semitransparent layer reflects grey or light of a color;it also absorbs certain wavelengths of light; and light is alsotransmitted through the semitransparent layer. One method of making thesemitransparent layer is by coating printing process inks on the back ofa transparent substrate in place of the opaque absorbing ink of theprior art. The thickness of the ink coatings determines the level oftransparency that can be anywhere from 0.1% to 99% for any givenwavelength. Alternatively, it is possible to use a commercial colorfilter like Roscolux™ brand of filters from Rosco Laboratories Inc., asthe back substrate; this will serve the same purpose as the coated ink.A semitransparent back layer enables a broader use for the writingtablet by employing templates, other sheet material, electronic skins,waveguides and even a digital display near the back layer to enable achangeable background for the display. Referring to FIG. 2, a writingtablet is constructed with upper transparent substrate 6 facing theviewer and a lower substrate 9 which is a color filter. Substrates 6 and9 are coated with transparent electrically conductive layers 5 and 3,respectively. A preferred conductor for the electrically conductivelayers is a conducting polymer because of its flexibility. Sandwichedbetween substrates 6 and 9 adjacent to the conductors is a cholestericliquid crystal dispersion 4 as for example described in U.S. PatentApplication Publication No. 2009/0033811, which is incorporated hereinby reference in its entirety. The dispersion 4 controls the flow of theliquid crystal with a polymer network to have the proper sensitivity tothe writing stylus. Instead of a dispersion, a polymer-free cholestericliquid crystal 4 may be used with spacers in high density in the spacebetween the electrodes to control flow and sensitivity as described inU.S. patent application Ser. No. 13/281,911, is incorporated herein byreference in its entirety. The color filter 9 is used as the bottomsubstrate, so that it is possible to view images on a template 10 orother objects placed behind the display 11. The semitransparent backlayer may be realized by coating inks on a transparent substrate such asthe 80 series inks from Norcote Corporation. The patterned layer ortemplate 10 can be lines to aid in writing text on the tablet or it canbe a figure such as a basketball court such as might be used by a coachto explain strategy and plays to his players. The template may also befigures for playing games or a learning aid for a child. The drivecircuitry is connected to the electrically conductive layers on ledges 7and 8 and can be identical to that described in U.S. Patent ApplicationPublication Nos. 2009/0033811 and 2009/0096942, which are incorporatedherein by reference in their entireties. The tablet can be driven inMode A or Mode B as described in those patent application publications.With such a coating there is a loss in contrast over the prior art thatutilizes a fixed opaque black back layer; however, this loss can belargely recovered with the template 10 that can be a replaceable colorinsert as will be described later. FIG. 2c further shows a top viewillustration of the template 10 being inserted under the tablet 11. Thetemplate 10 is optional as the display can be used without it or with avariety of other components besides the template 10 which are limitedonly by the imagination of the user, such as a photograph or painting.FIG. 2d shows the display that includes electrically conductive rows 17on the inside of one substrate and electrically conductive columns 18 onthe inside of the other substrate, the rows and columns being orthogonalto each other. This forms a passive matrix that can be driven to form animage as known in the art.

The display 11 of FIG. 2 can also be used without a template as there issignificant absorption from the semitransparent coating to enhance thecholesteric reflection contrast. To further enhance the contrast of thedisplay without a template, one can simply replace the template with aninsert that provides an opaque background. Surprisingly, the opaquebackground can be of any color or pattern even white. By changing thepattern or color of the removable background opaque insert one canchange the color or appearance of the display.

The color of the semitransparent ink and filters can be used incombination with a template of another color to change the contrast andcolor of the display. For example, if a blue coated display is placed ona red template, the result from color subtraction is a blue background.On the other hand when the same display is placed on a yellow template,the result is green background. This is because the color of the displaybackground is determined by the reflection of the remaining light afterabsorption by the coatings, filters and templates behind the liquidcrystal dispersion 4. Since the coatings are produced by eitherabsorptive filters or coated using absorptive inks, the displaybackground color is the result of color subtraction of the coating 9 andtemplate 10.

The color of the writing is determined by the additive mixing of theBragg reflection wavelength of the liquid crystal dispersion layer 4 andthe color reflected by the resultant color of the background. Forexample, if the cholesteric display is tuned to reflect yellow and ablue semitransparent background is used, the resultant writing fromcolor addition will be white. This color mixing of the background colorand the liquid crystal layer 4 is additive because there is noabsorption of the reflected color by the liquid crystal layer 4.

To increase the usability of the display 11, a case can be built to easethe placement of the template 10. An example would involve adhering thedisplay 11 to a rigid piece of semitransparent or clear plastic with aholding mechanism for the template 10. The holding mechanism can beeither, a removable glue, a mechanical fastener or simply a slot in theplastic that will allow the template to rest below the display. Thepiece of plastic separating the display 11 from the template can be ofany thickness including 0 mm, but the quality of the template imagewould suffer the further it is from the display 11.

Further, the display 11 described in FIG. 2 can be placed on areflective, backlit or emissive back display so that any image orpattern can be placed behind the display. Referring to FIG. 3, thedisplay 11 is placed on top of an electronic back display 14, which isin a dark state when there is no image on the screen. The back displaymay be a reflective, backlit or an emissive display. Images onreflective displays are visible because of ambient light interactingwith each of the display pixels and either getting reflected back orbeing absorbed. Therefore, to produce a dark image all the pixels areswitched so that all the incident light is absorbed. Displays that arebacklit produce images because the light behind each pixel is eithertransmitted to the viewer or not transmitted. To produce a dark image,all the pixels block the light from the backlight from reaching theviewer. In this case where there is no image and the screen is dark, thewriting tablet 11 has no pattern as illustrated in FIG. 3b . When astylus or finger nail is used to write an image on the display, theresult is a written image whose color depends on the additivity of thereflectivity of the cholesteric mixture in the dispersion layer 4 andthe color of the semitransparent coating. Referring to FIG. 3c , theelectronic back display 14 is displaying an image; this image showsthrough the writing tablet 11. Due to the location of thesemitransparent coating, the writing tablet performs better than adisplay with no coating, because the absorptive layer is closer to thecholesteric layer, hence enhancing the reflection of the writtentexture. The color of the image on the back display 14 showing throughthe writing tablet 11 will depend on the back semitransparent color 9and whether the back display 14 is emissive, reflective or backlit. Forexample, if the back display 14 is emissive or backlit, the color of thebackground showing through writing tablet 11 will be a result of thesubtraction of the original image color on the back display 14 after itgoes through the semitransparent ink on the writing tablet 11. Theemissive or backlit back display will have to be dimmed so that it doesnot overwhelm the contrast of the image written on writing tablet 11. Ifthe back display 14 is reflective, the image through the writing tablet11 will be of the same result as placing a template 10 under the writingtablet as described in FIG. 2 above. The writing tablet can also beplaced on a light guide like that which is sourced from Flashing LEDBoard™ through ledflashingboard.com sold as a Multi Color LED MessageBoard model #OCGDB1210. The light guide could have a pattern eitherpermanently etched on the top of it so as to allow light leakage ortemporarily marked so as to allow the same. Referring to FIGS. 4a and 4b, when the writing tablet 11 is placed on this light guide 15, there isno image showing through the writing tablet because the lights 16 neededto illuminate the pattern on the light guide are turned off. In FIG. 4c, the lights 16 are turned on and the image on the light guide 15 isilluminated and shows through the writing tablet 13.

Note that the light guide can be patterned in such a way that the wholebackground of the display can be illuminated. Using different coloredlights, the color of the background can be changed with a flick of aswitch.

The following sections of the specification, excluding the examples,have been excerpted and modified from U.S. patent application Ser. No.12/152,729, entitled “Multiple Color Writing Tablet,” which isincorporated herein by reference in its entirety. The main modificationis the fixed light absorbing layer of the '729 patent application can bereplaced by a semitransparent back layer and an optional patterned layercan be employed behind the semitransparent layer. Also, one option is toemploy at least one patterned ink layer in the writing tablet asdisclosed in the patent entitled “Electronic Display with PatternedLayer,”, U.S. Pat. No. 9,235,075, which is incorporated herein byreference in its entirety.

Cell Having Focal Conic Written Portion on Planar Background:

Another embodiment of this disclosure is a writing tablet in which thebackground state is the planar texture and the line created by thepressure of the stylus is in the focal conic texture. The bistablecholesteric writing tablet is illustrated in FIG. 6 and includessubstrates 250 of transparent, flexible material in which plastic ispreferred. The inner surface of the substrates are coated withtransparent conductive electrodes 260 from materials such an indium tinoxide (ITO) or a conducting polymer such as PEDOT. Sandwiched betweenthe adjacent electrodes is a bistable cholesteric material 320.

In FIG. 1, all of the electrodes and substrates are transparent, exceptfor the electrode and any substrate nearest to the light absorbing backlayer 1 (e.g., lower electrode 3 and lower substrate 2), which can betransparent or opaque. In FIG. 6 there is a semitransparent coating 310at the bottom of the display.

In this embodiment in which the liquid crystal is initially in theplanar texture, flow of the liquid crystal is not required for theinventive cell to form the focal conic texture using the pressure of astylus. The droplets can be confined as separate droplets within thedispersion or the droplets can be unconfined with interconnectingdroplets. The dispersions may be of the type prepared by water borneemulsions or by polymerization induced phase separation (PIPS) as isknown in the art. The image is created by the unique electro-opticcharacteristics of the cell rather than by flow to be described later.The conducting electrodes 260 are connected with electricalinterconnects 270 to electronic write (and erase) circuitry 330 thatprovides suitable voltages to the conducting electrodes 260, usually inthe form of a pulse, in order for pressure of the stylus to create animage.

In order to explain the function of the writing circuitry 330 of FIG. 6we turn to FIG. 7. FIG. 7 is an illustration of the typical andhypothetical voltage response shown as the Reflectance of the cellversus the Voltage of a pulse applied to the cell. There are two curvesillustrated in the voltage response of FIG. 7: a solid curve 350 for thecell with an undepressed cell gap 290 and a dashed curve 360 for areduced cell gap spacing 300 (the depressed and reduced cell gaps beingshown in FIG. 6). In both the solid 350 and the dashed 360 curves ofFIG. 7, the maximum light reflectance of the planar texture is indicatedby Rp 370 whereas the minimum light reflectance of the focal conictexture is indicated by Rfc 380. As illustrated in FIG. 7 the effect ofthe pressure from the stylus is to shift the voltage response from thesolid curve 350 to the dashed curve 360.

The procedure of writing an image on the inventive cell is to firsterase all previous images by applying an erasing voltage of value Vpindicated by vertical line 390 to drive the cell initially to the planartexture. The value of the voltage or magnitude of a voltage pulse to dothis is well known in the art of a bistable cholesteric liquid crystaldisplays; e.g., U.S. Pat. Nos. 5,453,863 and 5,691,795. This erases thewriting tablet to the reflective planar texture so that the backgroundcolor of the writing tablet is a color additive mixture of thereflective color of the cholesteric material 320 with the color of thesemitransparent back layer 310 of FIG. 6.

In order to write an image using stylus 280 a voltage, Vw, is applied bythe write circuit 330. The value of Vw is indicated by vertical line 400of FIG. 7. The voltage is applied for the duration of the stylus write;preferably a continuous AC voltage or a sequence of bipolar pulses. Thevoltage is applied to the patterned or unpatterned electrodes so thatthe entire display area of liquid crystal seen by the user of thewriting tablet, has an electric field applied to it. It is seen by curve360 in FIG. 7 that a voltage Vw 400 will drive that area of the cell tothe focal conic texture; that is, areas of the cell under the styluswhere pressure is applied and cell gap is reduced. The planar texture inthat area is driven to the focal conic texture as illustrated by thedashed curve 360. In the remainder of the cell where the cell gap is notdisturbed, even though the electric field has been applied here, thematerial will remain in the planar texture as indicated by the solidcurve 350, leaving a planar background for the focal conic writing. Inother words, the liquid crystal material where the cell gap isundisturbed remains in the planar texture as shown where line Vwintersects the solid line 350 (undepressed cell gap) while the voltageVw is applied to the electrodes and is not converted to the focal conictexture. The write circuit 330 can also provide an erasing voltage Vp toerase the entire tablet. It is seen by FIG. 7 that a voltage Vp 390 willdrive the entire cell to the planar texture, erasing the focal conicwriting. The voltage may be an AC voltage pulse or a sequence of pulses,preferably bipolar pulses.

References to writing “on a background” used in this disclosure meanswriting a black or color line on the writing tablet in which a majorityof the display area has the background color or is black, and does notmean that the background must be physically behind the writing or formedby a color of the light absorbing back layer. When the word “image” isused in this disclosure it means any black or color line and any blackor color background on the writing tablet, together with the design orpattern of the template 10 in FIG. 2, back display 14 in FIG. 3 orwaveguide 15 in FIG. 4. When we say “selecting a cell” or “writing on acell” in this disclosure, that means selecting the writing color toinclude the color reflected by that cell. It will be appreciated asdescribed above that the color of the display background and writingwill be affected by the color of the semitransparent ink 310 andtemplate 10 in FIG. 2, back display 14 in FIG. 3 or waveguide 15 in FIG.4.

II. Double Cell Writing Tablet:

We now turn to a second embodiment of the invention featuring amultiple-color tablet in which two active layers are stacked over eachother (FIG. 8). The active layers can be stacked such that each cellreflects a different planar reflective color and images can be writtenseparately on each cell with a single stylus to create multiple colorimages on the writing tablet. The cholesteric material of the cells eachhas a pitch length selected to reflect any color; preferably the colorsreflected by the two cells are different than each other. Primary suchreflective colors can be mixed to create a variety of colors subject tothe innovation of the user. The writing tablet enables a singleuntethered stylus to write or draw figures in different colors asselected by the user. Writing of different colors can be achieved in atleast two ways: a first Mode A in which planar texture color writing ispresented on a planar texture background; and a second Mode B in whichplanar texture color writing is presented on a focal conic background,preferably a color provided by the semitransparent ink layer. Each ofthese modes works on a different physical principle of the cholestericliquid crystal and will be described separately below.

The double cell writing tablet device can be made with either stackedseparate cells or as a single unit sharing substrates. The word “cell”as used herein means an active layer, the electrodes on either side ofit, and any substrates flanking the electrodes (i.e., on either side ofthe electrodes). In FIG. 8, completed cells 420 and 430 comprisingdifferent color active layers can be stacked as separate units eachhaving separate substrate 250 with an electrode 260 on an inside surfaceof it, the internal substrates 250 being joined with an index matchingmaterial 500 in between them. Likewise, the stacked cells can be made asa single unit that shares a common substrate between the active layers440 and 450, in which case the component structure having interiorelectrodes 260 on each interior substrate 250 with index matchingmaterial 500 between these substrates is replaced by a single substratedesignated 510 with two electrodes 260 disposed on either side of it.

IIa. Double Cell Writing Tablet in Mode A:

In describing Mode A, we refer to FIG. 8 which is an illustration of awriting tablet having double stack cells. The multiple-colordouble-stack tablet of FIG. 8 is made up of two cells, cell 420 stackedon top of cell 430. Cell 420 is of the same construction as cell 340 ofFIG. 6 containing transparent substrates 250 with transparent conductingelectrodes 260, connected to a writing circuit 330; however thesemitransparent ink coating 310 is absent. Cell 420 is stacked on top aswell as optically coupled to cell 430 so as to match the index ofrefraction of adjacent substrates. One means of optical coupling is witha thin layer of optical index matching fluid 500 between cells 420 and430. Cell 430 is also identical in construction to cell 340 of FIG. 6with transparent substrates 250 and transparent conducting electrodes260 that are electrically connected to writing circuit 330 as well ascontaining a semitransparent background coating 310.

Cells 420 and 430 are filled with a cholesteric liquid crystal material440 and 450, respectively. However, the cholesteric material within eachcell has a different reflective color than the other cell. For example,the liquid crystal of cell 420 may be a cholesteric material thatreflects blue light while the liquid crystal of cell 430 is acholesteric material that reflects yellow light. In certain applicationsit may be desired that materials 440 and 450 have a different handednessfor the helical twist; that is, one cell reflects right handed circularpolarization and the other left. Like the cholesteric material 320 ofFIG. 6, the cholesteric materials 440 and 450 of FIG. 8 are preferred tobe in the form of a polymeric dispersion. The droplets can be confinedas separate droplets within the dispersion since flow of the liquidcrystal is not required for this embodiment of the multiple colorwriting tablet. Materials 440 and 450, however, may also be a dropletdispersion in which the droplets are unconfined with interconnectingdroplets since flow will not affect its operation. The dispersions maybe of the type prepared by water borne emulsions or by polymerizationinduced phase separation as is known in the art.

A procedure of writing a multicolor image on the double stack tablet inMode A is to first erase all previous images by activating both writecircuits 460 and 470 to apply voltages of value Vp indicated by verticalline 390 (FIG. 7) to drive both cells 420 and 430 into the planartexture. The value of the voltage or magnitude of a voltage pulse to dothis is well known in the art of a bistable cholesteric liquid crystaldisplays; e.g., U.S. Pat. Nos. 5,453,863 and 5,691,795. This erases themulti-color writing tablet to the reflective planar texture so that thebackground color of the writing tablet is a color additive mixture ofthe reflective colors of the cholesteric materials 420 and 430 and anycolor of the semitransparent back layer 310.

In order to write an image of the color of the cholesteric 440 on thetop cell 420 by stylus 280 in Mode A, a voltage Vw must be applied bythe write circuit 470 of the bottom cell 430 during the writing process.The value of Vw is indicated by vertical line 400 of FIG. 7. The voltageis applied for the duration of the stylus write; preferably a continuousAC voltage or a sequence of bipolar pulses. It is seen by curve 360 ofFIG. 7 that a voltage Vw 400 will drive the bottom cell to the focalconic texture only in the vicinity of the stylus where pressure isapplied and the cell gap is reduced. This removes the planar texture ofthe liquid crystal 450 in the bottom cell 430 under the stylus (i.e., inreduced gap regions). In the remainder of the bottom cell 430 where thecell gap is not disturbed, the material will remain in the planartexture as indicated by the solid curve 350. Because no voltage isapplied to the electrodes for the upper cell 420, the liquid crystal 440of the upper cell is not changed from the planar texture. This forms animage composed of a written portion (region where pressure is applied bythe stylus to the writing surface) containing only the reflected lightof the color of the cholesteric 440 of top cell 420 (added with anycolor of the semitransparent coating 310, referred to as a “back color”)on a background color (formed by the undepressed (unwritten) regions ofboth cells) that is an additive mixture of the colors of the planartextures of both cells (along with any back color) in cooperation withthe template 10 in FIG. 2, back display 14 in FIG. 3 or waveguide 15 inFIG. 4.

In order to write an image of the color of the cholesteric 450 on thebottom cell 430 by stylus 280 in Mode A, a voltage Vw is applied by thewrite circuit 460 to the top cell 420 while the writing pressure isapplied to the writing surface. The value of Vw is indicated by verticalline 400 of FIG. 7. The voltage is applied for the duration of thestylus write; preferably a continuous AC voltage or a sequence ofbipolar pulses. It is seen by curve 360 of FIG. 7 that a voltage Vw 400will drive the cholesteric 440 of the top cell 420 to the focal conictexture in the vicinity of the stylus where pressure is applied (i.e.,at the written portion of the writing tablet) as the cell gap isreduced. In the remainder of the top cell where the cell gap is notdisturbed, the material will remain in the planar texture as indicatedby the solid curve 350. Therefore, the image will be composed of thewritten portion formed by colored light reflected from the planartexture of the cholesteric 450 of only the bottom cell 430 (added to anycolor of the back layer) in cooperation with the pattern or design ofthe template 10 in FIG. 2, back display 14 in FIG. 3 or waveguide 15 inFIG. 4. The written portion will be apparent on a background color(formed by the undepressed regions of both cells) that is an additivemixture of the colors of the planar textures of both cells (along withany background color) in cooperation with the design or pattern of thetemplate 10 in FIG. 2, back display 14 in FIG. 3 or waveguide 15 in FIG.4.

In Mode A, the write circuits 460 and 470 can be used to erase thetablet by providing a voltage Vp to each of cells 420 and 430. It isseen by FIG. 7 that a voltage Vp 390 will drive each of the cellsentirely to the planar texture. The voltage may be an AC voltage pulseor a sequence of pulses, preferably bipolar pulses.

IIb. Double Cell Writing Tablet in Mode B

In describing Mode B, we again refer to FIG. 8. The writing tablet isidentical to that described above except that the initial state of bothcells is focal conic and the cholesteric materials are in the form of apolymeric dispersion that will allow localized flow caused by thewriting pressure from a pointed instrument such as a pointed untetheredstylus to induce the planar texture. Droplets that are unconfined or areinterconnecting allow liquid crystal flow to occur under the pressure ofthe stylus 280 in reduced cell gap regions 480 and 490. Flow does notoccur and the liquid crystal texture does not change in undepressedregions 290.

A suitable voltage applied to the electrodes will drive the cholestericmaterial of both cells to the initial focal conic state (see FIG. 7).When viewed from above, the tablet will exhibit the color of thesemitransparent background coating 310 along with the template 10 inFIG. 2, back display 14 in FIG. 3 or waveguide 15 in FIG. 4 since thefocal conic texture is essentially transparent in this cellconfiguration. The pressure from the pointed stylus 280 in the locallyreduced cell gap spacing 480, 490 induces flow in the cholestericmaterial that changes the cholesteric texture from the transparent focalconic to the color reflective planar texture in the vicinity of the tipof the stylus 280. The stylus is used to draw an image similar todrawing with a pencil on paper. The written image can then be entirelyerased by applying a voltage pulse to the electrodes of sufficient valueto drive all the material to the focal conic state (see FIG. 7 and the'448 patent for suitable voltage to apply to each liquid crystal layer).

The procedure of writing a multicolor image on the double stack writingtablet of Mode B is to first erase all previous images by activatingboth write circuits 460 and 470 to apply voltages of value Vf indicatedby vertical line 410 of FIG. 7 to drive both cells 420 and 430 into thefocal conic texture. The value of the voltage or magnitude of a voltagepulse to do this is well known in the art of a bistable cholestericliquid crystal displays; e.g., U.S. Pat. Nos. 5,453,863 and 5,691,795.In order to write an image reflecting the color of the cholesteric 440on the top cell 420 only using stylus 280 a voltage Vw is applied by thewrite circuit 470 to the electrodes of the bottom cell 430 during thewriting process. The value of Vw is indicated by vertical line 400 ofFIG. 7. The voltage is applied for the duration of the stylus write;preferably a continuous AC voltage or a sequence of bipolar pulses. Thepurpose of the voltage is to maintain the focal conic texture of thebottom cell 430 under the action of the stylus (i.e., prevent formingthe planar texture in the written portion or depressed cell gap regionof the bottom cell). While this voltage is applied the pressure of thestylus does not induce a planar texture in cell 430 but maintains itsfocal conic texture during the writing process. The stylus does,however, induce a planar texture in the cholesteric 440 of the uppercell 420 in its vicinity (i.e., in the writing portion) that is believedto be due to lateral flow of the cholesteric liquid crystal in thereduced gap regions resulting in the focal conic texture beingtransformed to the planar texture. This occurs without any voltage beingapplied to the upper cell. Therefore, an image on a focal conicbackground, in cooperation with the patterned layer, on a stackedmulticolor cell is possible by suitably applying a voltage to allow theimage to be written on only one cell. The image is composed of thewriting portion at a color of the light reflected from the planartexture of the cholesteric 440 of the top cell 420 (added to any colorof the semitransparent back layer 310) on the unwritten and undepressedbackground (semitransparent back color of the back layer) in cooperationwith the template 10 in FIG. 2, back display 14 in FIG. 3 or waveguide15 in FIG. 4.

Similarly, in order to form an image on the bottom cell 430 only bystylus 280 a voltage Vw must be applied by the write circuit 460 to theelectrodes of the top cell 420 during the writing process. As before,both cells are initially in the focal conic texture. The value of Vw isindicated by vertical line 400 of FIG. 7. The voltage is applied for theduration of the stylus write; preferably a continuous AC voltage or asequence of bipolar pulses. The purpose of the voltage is to maintainthe focal conic texture of the top cell 420 under the action of thestylus. While this voltage is applied the pressure of the stylus doesnot induce a planar texture in top cell 420 but maintains its focalconic texture from the erasure process. The stylus does, however, inducea planar texture in the bottom cell 430 due to induced lateral flow ofthe cholesteric liquid crystal (without applying voltage to the bottomcell), resulting in the focal conic texture being transformed to theplanar texture in the reduced cell gap region of the bottom cell (i.e.,in the written portion). This produces an image composed of the writingportion at a color of the light reflected from the planar texture of thecholesteric 450 bottom cell 430 (added to any color of thesemitransparent back layer 310) on the unwritten and undepressedbackground (semitransparent back color of the back layer) in cooperationwith the template 10 in FIG. 2, back display 14 in FIG. 3 or waveguide15 in FIG. 4. Therefore, a planar image on a focal conic background canbe selectively written separately on each cell of the stack to produce amultiple color image.

IIe. Multimode Double Cell Writing Tablet:

The inventive writing tablet can also be designed so that one of thecells operates according to Mode A and the other cell operates accordingto Mode B. That is, one cell has an initial planar texture while theother cell has the initial focal conic texture. Writing in a color ofonly one of the cells (added to any back color) in cooperation with thetemplate 10 in FIG. 2, back display 14 in FIG. 3 or waveguide 15 in FIG.4 is selected by applying the write voltage Vw to the other cell whilewriting pressure is applied. The background will have the color of theundepressed regions of the planar cell (added to any back color) incooperation with the template 10 in FIG. 2, back display 14 in FIG. 3 orwaveguide 15 in FIG. 4. For example, when a first cell desired to beselected is in the initial focal conic texture, the other second cell inthe planar texture has the writing voltage Vw applied during the writingprocess. The planar texture is erased from the second layer in thewritten portion where the cell gap is reduced, as Vw is applied. Thewriting process forms the planar texture in the written portion of thefirst layer where the cell gap is reduced. The resulting image will bethe written portion at the planar texture of the first layer only (addedto any semitransparent background color) on a background formed by theplanar texture of undepressed regions of the second layer (added to anysemitransparent background color). Both the written portion andbackground cooperate with template 10 in FIG. 2, back display 14 in FIG.3 or waveguide 15 in FIG. 4.

Another way to form an image on the multimode, two layer writing tabletis by applying the write voltage to both cells, in effect, selecting thebackground. Upon writing, the planar texture is prevented from beingformed in the written portion of the focal conic layer and the planartexture is erased to the focal conic in the written portion of theplanar layer. This forms an image composed of a written portion in blackor any back color on a background of the color reflected by the planarlayer (added to any background color). The written portion andbackground cooperate with the template 10 in FIG. 2, back display 14 inFIG. 3 or waveguide 15 in FIG. 4.

Yet another way to form an image on the multimode, two layer writingtablet is by not applying the write voltage to either layer. The writingprocess will form the planar texture in the written portion of the focalconic layer and will not affect the planar texture existing in thewritten portion of the other planar layer. This will result in an imagethat is the addition of the colors reflected from both layers in theirwritten portions (along with any semitransparent back color) on abackground that is the color of light reflected from the planar layer(added to any semitransparent back layer color). Both the writtenportions and background cooperate with the template 10 in FIG. 2, backdisplay 14 in FIG. 3 or waveguide 15 in FIG. 4.

It should be apparent from the foregoing that the cells can be designedthe same or differently by changing the liquid crystal dispersion. Inthe initially planar cell, liquid crystal flow is not needed to changethe planar texture to the focal conic in the layer where the writingvoltage is applied. Therefore, the liquid crystal of this cell can be inconfined droplets or in a dispersion of liquid crystal in a polymermatrix that does not encapsulate or confine the liquid crystal enablingit to flow. However, the liquid crystal in the initially focal coniccell must be in a dispersion that enables it to flow upon application ofpressure from a pointed stylus. This allows the writing tablet to beformed from cells using different combinations of liquid crystaldispersions. For example, a writing tablet could be made so that bothcells only have confined droplets of liquid crystal material in apolymer matrix using a PIPS process and will only operate in Mode Aonly. A writing tablet formed of unconfined droplets in both cells, or awriting tablet having a focal conic cell having unconfined droplets andconfined or unconfined liquid crystal in the planar cell, could operatein Mode A, Mode B or in as a multimode writing tablet.

It should be appreciated in reading this disclosure that the writingtablet of this disclosure can have more than two liquid crystal layersas in the case of a triple stack display disclosed in the Ser. No.12/152,729 patent application, which can have liquid crystal layersreflecting red, green and blue, respectively, in any order.

The description will now refer to the following examples which shouldnot be used to limit the broad invention as described by the claims.

Example 1

A Boogie Board™ writing tablet purchased from a Brookstone retail storewas disassembled so that the opaque coating from the back substratecould be removed. The removal of the ink was done using a methanol wipe.After cleaning, the display was coated with Norcote brand blue processink, forming the semitransparent back layer. Once the ink was dried, thedisplay and electronics were assembled on a thin sheet of clear acrylic.The result of this process changes the display from a writer with yellowwriting on a black background to one with yellow writing on asemitransparent blue background. A photograph of the resulting writingtablet is shown in FIG. 5A. FIG. 5B shows a side view of the writingtablet photographed in FIG. 5A including a representative article (ahand 802) over which the writing tablet is placed for viewing thearticle. The article is free of attachment to the writing tablet. Thewriting tablet includes the components 11 (e.g., as in FIG. 2), and theoptional polymer layer 801 made of acrylic. The bottom of the writingtablet can be formed by the semitransparent back layer of the component11, or by the polymer layer 801 which could be clear or semitransparent.

Example 2

In FIG. 9, the reflection spectra of a solid yellow template is shown bythe solid line. When a writing tablet with blue semitransparentbackcoat, operating in the B mode, is placed on the template, the regionwith no writing (focal conic or dark state) has a reflection spectrashown by the dotted line. This resultant spectra is due to colorsubtraction of the yellow template spectra by the blue semitransparentcoating that cut off most of the reflected light beyond 500 nm and alsoabsorption of some of the light by the template in wavelengths less than450 nm. The written region would show a reflection spectra shown by thedashed line, which includes the result of color subtraction of theyellow template and blue coating in cooperation with color addition dueto the liquid crystal layer reflecting light between 485-640 nm.

Example 3

In FIG. 10, the reflection spectra of a solid white template is shown bythe solid line. When a writing tablet with blue semitransparentbackcoat, operating in the B mode, is placed on the template, the regionwith no writing (focal conic) has a reflection spectra shown by thedotted line. This resultant spectra is due to color subtraction of thewhite spectra by the blue semitransparent coating that cut off most ofthe reflected light beyond 550 nm and lets about 30% of the light ataround 475 nm. The written region would show a reflection spectra shownby the dashed line, which includes the result of color subtraction fromthe blue coating in cooperation with color addition due to the liquidcrystal layer reflecting light between 485-640 nm.

FIG. 11 shows an article generally represented by 600 includingelectronic skin liquid crystal display 11 of this disclosure. Thearticle 600 is selected from the group consisting of cell phone, laptop,computer, computer monitor, computer mouse, computer keyboard,television, I-pod, MP3 player, PDA, video game controller, stereo,radio, CD player, appliance, toy, headphones, clock, handheld electronicdevices, key ring accessory, shoe, purse, backpack, briefcase, computercase, computer covering, jewelry, watch, bottle, bottle lid, clothing,clothing embellishment, furniture, furniture embellishment, mobileentertainment case and combinations thereof.

FIGS. 12a and 12b show an electronic display of this disclosureincluding a semitransparent back layer showing any removable backpattern generally depicted by 601 used behind it, such as one includingnotepad lines, for example, graph paper.

FIG. 13 is the same as FIG. 8 but shows three cholesteric liquid crystalcomponents 703, 420 and 430. The figure differs from FIG. 8 in theaddition of upper component 703 which includes liquid crystal layer 704sandwiched between transparent substrates 250, the substrates includingelectrically conductive layers 260 on their inside surfaces, the liquidcrystal being driven or erased by write circuit 701. The other featuresof the display are the same as discussed above in connection with FIG. 8with the same elements having the same reference numbers. The liquidcrystal layers 704, 440, 450, reflecting a different one of red, greenand blue, in any order. The semitransparent layer 310 is disposed behindthe three stacked liquid crystal layers and other indicated components.

Many modifications and variations of the invention will be apparent tothose of ordinary skill in the art in light of the foregoing disclosure.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention can be practiced otherwise than has beenspecifically shown and described.

What is claimed is:
 1. An electronic display comprising: electricallyconductive layers; an active layer disposed between adjacent saidelectrically conductive layers, said active layer including cholestericliquid crystal material; a transparent front substrate disposed adjacentone of said electrically conductive layers near a front of said display;a semitransparent back layer that absorbs light that passes through saidactive layer, reflects grey light or light of a color and is lighttransmitting, wherein said semitransparent back layer comprises one of:ink coated on a transparent substrate; and a transparent substrateincluding ink; wherein said semitransparent back layer forms a bottomsurface of said display, or a semitransparent or clear layer below saidsemitransparent back layer forms a bottom surface of said display; andelectronic circuitry for applying a voltage to said electricallyconductive layers that enables at least one of erasing or writing ofsaid active layer.
 2. The electronic display of claim 1 comprising threeof said active layers which reflect red, green and blue light,respectively, each of said active layers being disposed between adjacentsaid electrically conductive layers.
 3. An electronic displaycomprising: electrically conductive layers; an active layer disposedbetween adjacent said electrically conductive layers, said active layerincluding cholesteric liquid crystal material; a transparent frontsubstrate disposed adjacent one of said electrically conductive layersnear a front of said display; a semitransparent back layer that absorbslight that passes through said active layer, reflects grey light orlight of a color and is light transmitting, wherein said semitransparentback layer comprises ink or a colored filter; wherein saidsemitransparent back layer forms a bottom surface of said display, or asemitransparent or clear layer below said semitransparent back layerforms a bottom surface of said display; and electronic circuitry forapplying a voltage to said electrically conductive layers that enablesat least one of erasing or writing of said active layer; wherein saiddisplay is adapted to be used with a back pattern that is removablydisposed behind said semitransparent back layer, wherein said backpattern is visible through said semitransparent back layer.
 4. Theelectronic display of claim 3 wherein said back pattern comprises awaveguide including light sources disposed at an edge thereof, and lightemitting portions on a surface of said waveguide enabling light to leavesaid waveguide in a pattern.
 5. The electronic display of claim 3wherein said back pattern comprises an emissive, backlit or reflectivedisplay device for displaying images.
 6. The electronic display of claim3 wherein said back pattern is removably held to said electronicdisplay.
 7. The electronic display of claim 3 wherein saidsemitransparent back layer includes one color, said active layerincludes said cholesteric liquid crystal that reflects another color andsaid back pattern includes yet another color.
 8. The electronic displayof claim 3 wherein said back pattern is selected from the groupconsisting of: a template of a sports field, court or arena, a patternfor a children's game, an image for children to color, notepad lines,graph paper lines, and a menu of items that one can choose from.
 9. Anelectronic display comprising: electrically conductive layers; an activelayer disposed between adjacent said electrically conductive layers,said active layer including cholesteric liquid crystal material; atransparent front substrate disposed adjacent one of said electricallyconductive layers near a front of said display; a semitransparent backlayer that absorbs light that passes through said active layer, reflectsgrey light or light of a color and is light transmitting, wherein saidsemitransparent back layer comprises ink or a colored filter; whereinsaid semitransparent back layer forms a bottom surface of said display,or a semitransparent or clear layer below said semitransparent backlayer forms a bottom surface of said display; and electronic circuitryfor applying a voltage to said electrically conductive layers thatenables at least one of erasing or writing of said active layer; whereinsaid display is adapted to be placed over a variety of articles forviewing, the articles being free of attachment to said display.
 10. Awriting device comprising: electrically conductive layers; at least oneactive layer disposed in a gap between adjacent said electricallyconductive layers, said active layer including bistable cholestericliquid crystal material; an outer layer of flexible transparent materialforming a writing surface; wherein said active layer is adapted toenable writing pressure applied to said writing surface to reducethickness of said gap to form a reduced gap region in which the liquidcrystal is light reflecting so as to reflect light of a color or isessentially transparent, a texture of said liquid crystal beingunchanged in a non-reduced gap region; and a semitransparent back layerthat absorbs light that passes through said active layer, reflects greylight or light of a color and is light transmitting, wherein saidsemitransparent back layer comprises one of: ink coated on a transparentsubstrate; and a transparent substrate including ink; wherein saidsemitransparent back layer forms a bottom surface of said writingdevice, or a semitransparent or clear layer below said semitransparentback layer forms a bottom surface of said writing device.
 11. Thewriting device of claim 10 comprising electronic circuitry for applyinga voltage to said electrically conductive layers that enables at leastone of erasing or writing of said active layer.
 12. The writing deviceof claim 11 wherein said electronic circuitry applies a writing voltageto said electrically conductive layers, said writing pressure beingapplied while applying said writing voltage effective to place saidreduced gap region of said active layer in said essentially transparentfocal conic texture while not changing said texture of an unreduced gapregion of said active layer.
 13. The writing device of claim 10comprising three of said active layers which reflect red, green and bluelight, respectively, each of said active layers being disposed betweenadjacent said electrically conductive layers.
 14. The writing device ofclaim 10 comprising electronic circuitry for applying a voltage to saidelectrically conductive layers that enables at least one of erasing orwriting of said active layer and wherein said writing device is adaptedto be used with a back pattern that is removably disposed behind saidsemitransparent back layer, wherein said back pattern is visible throughsaid semitransparent back layer.
 15. The writing device of claim 10comprising one of said electrically conductive layers forming rows ofsubstantially parallel electrode lines on one side of said active layerand another of said electrically conductive layers forming columns ofsubstantially parallel electrode lines on the other side of said activelayer, wherein said columns are substantially orthogonal to said rows.16. An article comprising the writing device of claim 10 selected fromthe group consisting of laptop, computer, computer monitor, computermouse, computer keyboard, television, I-pod, MP3 player, PDA, video gamecontroller, stereo, radio, CD player, appliance, toy, headphones, clock,handheld electronic devices, key ring accessory, shoe, purse, backpack,briefcase, computer case, computer covering, jewelry, watch, bottle,bottle lid, clothing, clothing embellishment, furniture, furnitureembellishment, mobile entertainment case and combinations thereof.
 17. Awriting device comprising: electrically conductive layers; at least oneactive layer disposed in a gap between adjacent said electricallyconductive layers, said active layer including bistable cholestericliquid crystal material; an outer layer of flexible transparent materialforming a writing surface; wherein said active layer is adapted toenable writing pressure applied to said writing surface to reducethickness of said gap to form a reduced gap region in which the liquidcrystal is light reflecting so as to reflect light of a color or isessentially transparent, a texture of said liquid crystal beingunchanged in a non-reduced gap region; and a semitransparent back layerthat absorbs light that passes through said active layer, reflects greylight or light of a color and is light transmitting, wherein saidsemitransparent back layer comprises ink or a colored filter; whereinsaid semitransparent back layer forms a bottom surface of said writingdevice, or a semitransparent or clear layer below said semitransparentback layer forms a bottom surface of said writing device; wherein saidwriting device is adapted to be used with a back pattern that isremovably disposed behind said semitransparent back layer, wherein saidback pattern is visible through said semitransparent back layer.
 18. Thewriting device of claim 17 wherein said back pattern comprises awaveguide including light sources disposed at an edge thereof, and lightemitting portions on a surface of said waveguide enabling light to leavesaid waveguide in a pattern.
 19. The writing device of claim 17 whereinsaid back pattern comprises an emissive, backlit or reflective displaydevice for displaying images.
 20. The writing device of claim 17 whereinsaid back pattern is removably held to said writing tablet.
 21. Thewriting device of claim 17 wherein said semitransparent back layerincludes one color, said active layer includes said cholesteric liquidcrystal material that reflects light of another color and said backpattern includes yet another color.
 22. The writing device of claim 17wherein said back pattern is selected from the group consisting of: atemplate of a sports field, court or arena, a pattern for a children'sgame, an image for children to color, notepad lines, graph paper lines,and a menu of items that one can choose from.
 23. A writing devicecomprising: electrically conductive layers; at least one active layerdisposed in a gap between adjacent said electrically conductive layers,said active layer including bistable cholesteric liquid crystalmaterial; an outer layer of flexible transparent material forming awriting surface; wherein said active layer is adapted to enable writingpressure applied to said writing surface to reduce thickness of said gapto form a reduced gap region in which the liquid crystal is lightreflecting so as to reflect light of a color or is essentiallytransparent, a texture of said liquid crystal being unchanged in anon-reduced gap region; and a semitransparent back layer that absorbslight that passes through said active layer, reflects grey light orlight of a color and is light transmitting, wherein said semitransparentback layer comprises ink or a colored filter; wherein saidsemitransparent back layer forms a bottom surface of said writingdevice, or a semitransparent or clear layer below said semitransparentback layer forms a bottom surface of said writing device; wherein saidwriting device is adapted to be placed over a variety of articles forviewing through said semitransparent back layer, the articles being freeof attachment to said writing device.
 24. An electronic displaycomprising: electrically conductive layers; an active layer disposedbetween adjacent said electrically conductive layers, said active layerincluding cholesteric liquid crystal material; a transparent frontsubstrate disposed adjacent one of said electrically conductive layersnear a front of said display; a semitransparent back layer that absorbslight that passes through said active layer, reflects grey light orlight of a color and is light transmitting, wherein said semitransparentback layer comprises a colored filter and a lower one of saidelectrically conductive layers is in contact with said colored filter;wherein said semitransparent back layer forms a bottom surface of saiddisplay, or a semitransparent or clear layer below said semitransparentback layer forms a bottom surface of said display; and electroniccircuitry for applying a voltage to said electrically conductive layersthat enables at least one of erasing or writing of said active layer.25. An electronic display comprising: electrically conductive layers; anactive layer disposed between adjacent said electrically conductivelayers, said active layer including cholesteric liquid crystal material;a front substrate disposed adjacent one of said electrically conductivelayers near a front of said electronic display; a semitransparent backlayer that absorbs light that passes through said active layer, reflectsgrey light or light of a color and is light transmitting; wherein saidsemitransparent back layer forms a bottom surface of said electronicdisplay, or a semitransparent or clear layer below said semitransparentback layer forms a bottom surface of said electronic display; andelectronic circuitry for applying a voltage to said electricallyconductive layers that enables at least one of erasing or writing ofsaid active layer, wherein writing formed on said cholesteric liquidcrystal material contrasts with said semitransparent back layer and saidsemitransparent back layer is see through.
 26. The electronic display ofclaim 25 wherein said front substrate is transparent and flexible andsaid active layer includes a dispersion of said cholesteric liquidcrystal material and polymer, wherein pressure applied to said frontsubstrate changes a reflectance of said cholesteric liquid crystalmaterial to form the writing.
 27. The electronic display of claim 25wherein said semitransparent back layer includes a colored polymericlayer or a polymeric layer including a colored coating on a surface ofsaid polymeric layer.
 28. The electronic display of claim 25 whereinsaid semitransparent back layer includes a colored filter.